The evolution of cellular communications has resulted in a proliferation of networks of different technologies and corresponding different air interfaces. As a result, during the course of a single call, a wireless mobile station may roam among multiple networks, wherein each such network implements a different technology than the other networks of the multiple networks. Among the different network technologies are high rate packet data (HRPD) Code Division Multiple Access (CDMA) technologies, such as CDMA 2000 1XEV-DO (1X Evolution Data Optimized) or packet switched CDMA 1XRTT (1X Radio Transmission Technology), that are capable of providing high rate packet data communication services, and conventional, or legacy, CDMA cellular communication technologies, such as a CDMA 1X.
As the mobile station roams among a HRPD CDMA communication network and a legacy CDMA communication network, it may be beneficial to system performance to handoff the mobile station from the former network to the latter network or from the latter network to the former network. For example, the channel conditions associated one such network may be more favorable than the channel conditions associated with the other such network due to such factors as fading, adjacent and co-channel interference, and available power at a serving base station (BS) or radio access network (RAN). By way of another example, an operator of both a packet switched CDMA network and a circuit switched CDMA network may desire to move the mobile station from one such network and to the other such network for purposes of system loading.
Currently, the only defined method for executing a handoff between a HRPD CDMA network and a legacy CDMA network is an execution of a dormant hard handoff, wherein a mobile station must go dormant and drop a radio resource of a network of a first CDMA technology and then acquire a radio resource of a network of a second CDMA technology. A result is a brief period of time during which the mobile station is not actively engaged in a communication session with either network. Further, when executing a dormant hard handoff there is no linkage between the two networks as the mobile station must drop the first network and acquire the second network without any assistance from the BS or RAN of either network. As a result, voice/data traffic may be lost during the handoff, resulting in poor system performance and efficiency and disgruntled end users.
Therefore, a need exists for a method and apparatus for an active hard handoff of a communication session between a legacy CDMA network and a high rate packet data CDMA 2000 network that minimizes an amount of time that a mobile station is not actively engaged in a communication session with either network during a handoff.